Josh Gad, Andrew Rannells Star

As backers’ auditions go, “Gutenberg! The Musical!” — a wildly delusional conceit so full of itself that it boasts two exclamation points — doesn’t stand a chance of making it to Broadway. That is, unless it can convince an audience of potential producers that it is witnessing the greatest creation since, well, the printing press.

It greatly helps that this starry-eyed writer-composer duo from Nutley, New Jersey who are desperately selling their show — emphasis on desperately — are played by Josh Gad and Andrew Rannells, reunited 12 years after their terrific pairing in “The Book of Mormon.” It almost makes it all worthwhile — almost.

But meta-musicals have lost a bit of their winking novelty since this show began nearly 20 years ago, first as an extended 45-minute sketch for the Upright Citizens Brigade, then later for an Off Broadway run starting in 2006, followed by regional productions.

It took the reuniting of this premium comedic duo to give it the clout to get the show to Broadway (for real) for this limited run. Once again, the show is directed by that master stager of challenging properties, Alex Timbers, who helmed the original Off Broadway gig.

Scott Brown and Anthony King, who wrote the book and songs for the show (and were scripters for the wickedly clever “Beetlejuice” musical) fill their outlandish premise with loopy humor, insider jokes and simple silliness from the get-go — up to the sweet and surprising twist of the ending.

The stakes are high for Bud Davenport (Gad) and Doug Simon (Rannells), old buddies who have pooled their family inheritances to rent a Broadway theater (with parking). They’re backed by three members of Middlesex, New Jersey’s premier wedding band, The Middlesex Six, for this one-night-only pitch to producers. (“So as you can see, we need this to go well,” says Bud. “It has to,” deadpans Doug with a whiff of fear.)

The two explain to the audience (here positioned as potential investors) that in their quick Google search on the 15th-century German inventor they found scant information, so they simply embellished their subject with “historical fiction.” (“It’s fiction… that’s true,” says Bud.)

Setting their story in the fictional town of Schlimmer (amid Scott Pask’s bright hodgepodge set), the two wannabes have made Gutenberg a wine-presser by trade, creating a conflict between the inventor’s desire to make the local populace literate and a mad monk’s power-hungry desire to continue interpreting the Bible for his own medieval purposes.

The rest of the show-within-a-show’s narrative is as demented as it is inaccurate, with the two actors playing all of the roles and their very movable types, from slobbering drunks to a coquettish ingenue named Helvetica.

At first, all off the goings-on are entertaining in a crazy kind of way — until they become less and less so. The serviceable songs and uninspired lyrics never rise to any comedic heights; the schtick of the actors wearing dozens of caps — with the names of the multiple characters emblazoned on them — quickly grows tiresome; and the faux Gutenberg story, for all its wackiness, is just not that engaging, especially as the show stretches into a second act.

The real fun, however — and there is much of it — lies in simply watching Gad and Rannells run riot, riff with each other, play with the audience, and just have a grand old time once again playing sweet, deluded dreamers. With their simpatico rhythms, the two demonstrate the art of great comedic pairings: Rannells’ tightly-wound, cool earnestness perfectly counterbalances Gad’s hot-mess of anxieties. (Both are nicely costumed by Emily Reboltz, with neat argyles for Rannells and rumpled everything for Gad.)

In the end, it’s not “Gutenberg” the show but rather this odd coupling of comedic pals, both on stage and off, that delights. Hats off to them.